Fuel injection systems for internal combustion engines may include pressure sensors to provide feedback of fuel pressure to a fuel control system so that a desired fuel pressure may be provided to an engine. Since the amount of fuel injected to an engine may be affected by a pressure at which the fuel is delivered, it may be desirable to confirm that fuel is being provided at a desired pressure. If fuel is not provided at the desired pressure, engine emissions and performance may degrade. Further, it may be desirable to limit engine air charge during such conditions to limit engine torque. Therefore, it may desirable to ascertain whether or not fuel is being delivered at the desired pressure and whether or not the fuel pressure sensor is operating in a desired manner. One way to confirm fuel pressure sensor operation is to provide multiple fuel sensors to measure fuel pressure. However, providing multiple fuel pressure sensors that provide substantially the same function can increase system cost. Additionally, fuel pressure sensors may be selected to provide pressure readings over a large span of pressures. Consequently, output from the pressure sensors may not provide as much resolution as is desired for relatively small changes in fuel pressure.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method for monitoring engine fuel pressure, comprising: commanding a first actuator to cause a change in fuel pressure; adjusting a second actuator in response to a change in fuel temperature that occurs from commanding the actuator to cause a change in fuel pressure; and limiting cylinder air charge to less than a threshold via the second actuator.
In this way, output from a fuel temperature sensor may sense fuel temperature at times when fuel temperature can be converted in to a variable that is indicative of fuel pressure. Further, the variable can be compared against output of a pressure sensor to determine if there is a desired correlation between the pressure sensor output and the temperature sensor output. In one example, fuel pressure is inferred from fuel pressure based on adiabatic compression of the fuel and cylinder air charge is limited when there is a disagreement between fuel pressure estimates.
The present description may provide several advantages. Specifically, the approach may reduce system cost while providing redundant sensing of fuel pressure. Further, the approach may be useful for identifying degradation of temperature or pressure sensors. Further still, the approach may be implemented in existing fuel systems without having to extensively redesign the fuel systems.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.